Controlling spray guns

ABSTRACT

A solvent pressure controlling device is included in the solvent delivery line to a solvent delivery port arranged to be connected with a spray gun through a single hose during disconnection of the hose from one paint delivery port preparatory to connection with another paint delivery port. Said device is operable while the hose connects the gun with the solvent delivery port to maintain the rate of emission from the gun of residual paint in the hose at a pressure substantially the same as that at which paint is emitted from the gun when the hose connects the gun to a paint delivery port.

' [451 Sept. 5, 1972 [54] CONTROLLING SPRAY GUNS [72] Inventor: Howard Richard James Knight, Hampton, England [73] Assignee: Carrier Engineering Company Limited, London, England 22 Filed: July 26, 1971 21 Appl.No.: 165,993

[30] I Foreign Application Priority Data July 29, 1970 Great Britain ..36,783/70 [56] References Cited UNITED STATES PATENTS Fleming ..239/305 X 8/ 1964 Herklotz et al. ..239/304 X 3/1966 Barrows ..239/1 12 X Primary ExaminerM. Henson Wood, Jr. Assistant ExaminerEdwin D. Grant Attorney-Snyder, Brown & Ramik [57] ABSTRACT A solvent pressure controlling device is included in the solvent delivery line to a solvent delivery port arranged to be connected with a spray gun through a single hose during disconnection of the hose from one paint delivery port preparatory to connection with another paint delivery port. Said device is operable while the hose connects the gun with the solvent delivery port to maintain the rate of emission from the gun of residual paint in the hose at a pressure substantially the same as that at which paint is emitted from the gun when the hose connects the gun to a paint delivery port.

10 Claims, 2 Drawing Figures PATENTEDSEP 51972 SHEET 2 0F 2 CONTROLLING SPRAY GUNS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for controlling a spray gun in the automatic painting of a succession of articles, for example automobile bodies, with paints of different colors.

2. Description of the Prior Art.

The automatic painting of articles, as above-mentioned, depends, among other things, upon paint being sprayed from a gun nozzle at a given emission rate according to the film thickness of paint required, the size of the articles, and the speed of a conveyor by which positioned remote from the spray gun, a length of hose is necessary to connect the device to the spray gun. If this is a long hose, such as is usually the case when painting automobile bodies, for example the hose has a length of 20 feet, the amount of paint which would be wasted during purging preparatory to the delivery of paint of a different color would, apart from other factors, render the device uneconomical in use. It is, therefore, necessary to program the change of color before the end of a painting cycle so that most of the paint can be utilized.

In US. Pat. No. 3,128,787, Howard Richard James Knight, there is described an apparatus for controlling the operation of a spray gun in which a single hose connected to the gun is arranged to connect the gun to any one of a plurality of paint delivery ports and with a solvent delivery port from which solvent is delivered to the gun during disconnection of the hose from one paint delivery port and connection of the hose with another of the paint delivery ports. With such an apparatus it is desired that the initial pressure of the solvent must be approximately the same as that of the paint so as to force the paint through the nozzle of the spray gun and maintain the emission rate. Because, however, the paint is of higher viscosity than the solvent as the proportion of solvent and paint in the hose changes the applied pressure must be progressively reduced to compensate for the reduced frictional resistant of progressively less paint and it is a main object of the invention to provide an apparatus for producing this effect.

SUMMARY According to the invention there is provided apparatus for controlling the operation of a spray gun, comprising a single hose connected to the gun and arranged to connect the gun to any one of a plurality of paint delivery ports and with a solvent delivery port from which a solvent is delivered to the gun during disconnection of the hose from one paint delivery port and connection of the hose with another of the paint delivery ports, and a solvent pressure controlling device included in a solvent delivering line to the solvent port and operable when the hose connects the solvent delivery port with the hose to maintain the rate of emission from the gun of residue paint in the hose at a pressure substantially the same as that at which paint is emitted from the gun when the hose connects the gun to a paint delivery port.

In one embodiment of the invention the solvent pressure controlling device comprises a cylinder, a piston slidable axially within the cylinder between stops determining the stroke of the piston thereby to form in the cylinder gas and solvent chambers on opposite sides of the piston, a solvent inlet to the solvent chamber connectable with a source of solvent, a solvent outlet from the solvent chamber connectable with said solvent delivery port, control means operable to control the flow of solvent to the solvent chamber to urge the piston into the. gas chamber, and connector means connectable with a source of pressurized gas and arranged to admit gas to the gas chamber thereby to feed the solvent through the solvent outlet thereby to effect said emission from the gun of residue paint in the hose.

In one embodiment of the invention the connector means includes a plug adjustable axially of the cylinder to determine the volume of the gas chamber. The connector means preferably also includes a solenoidoperated pneumatic valve preceded by a gas regulator. The stops may be located in the plug and one of the stops be adjustable axially of the plug to determine the volume of the solvent chamber. The apparatus preferably also includes a spring tending to urge the piston towards the solvent chamber and to exert on the piston a pressure approximately that of the frictional forces of the piston on the walls of the cylinder.

The control means may comprise a solenoidoperated pneumatic valve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 diagrammatically illustrates apparatus according to the invention applied to a device for controlling the delivery of paints of different colors to spray guns, and

FIG. 2 is a section through a part of the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates diagrammatically, a part of the apparatus described in the specification of US. Pat. application Ser. No. 67,869,

' Howard Richard James Knight, for controlling the operation of spray guns. Only so much of the apparatus as is necessary to the understanding of the present invention will be described herein.

As illustrated in FIG. 1 there is shown a selector and valve device 1 having 20 inlet ports, a number of which are indicated at 2, arranged around a circle 3. Each one of 18 of these ports, of which those numbered 4, 5, 6, 21 are illustrated, is connected via individual hoses, not shown, to a source of paint of a different color from the others. The port indicated at 22 is connected via a separate hose to a supply of solvent. A compressed gas v supply, which in the embodiment being described is air, may be connected to a delivery hose 31 referred to below. In the embodiment being described the port 23 is not used and is suitably blanked off.

A radially extending tubular selector arm is attached to a pinion 26 which co-operates with a rack 27 in such a way that longitudinal movement of the rack causes the arm 25 to rotate and one end 28 of the arm 25 to move over the twenty ports. The end of the tubular arm 25 is so designed that it co-operates with a sealing face associated with each of the inlet ports to provide a fluid-tight seal between a respective port and the tubular arm 25. Aflat annulus, indicated by the dotted line 29, extends on either side of the arm 25 and rotates with the arm 25,.co-operating with the sealing face to seal each of the ports not coupled to the arm 25. The other end 30 of the tubular arm 25 is coupled to a delivery hose, indicated by the dotted line 31, providing a feed to spray guns 32 and 33. A path may thus be selected and opened between any one of the supplies of paint, or of the supply of solvent, and the spray guns, and the source of compressed gas be connected to the hose 31 at a position between the valve 1 and the spray guns and preferably close to the valve 1.

Thus far the apparatus is substantially as illustrated in the drawings accompanying the specification of US. Pat. application Ser. No. 67,869,I-Ioward Richard James Knight, and is controlled by a programming unit in the manner described in that Specification.

The apparatus according to the present invention for maintaining the emission rate of residual paint of one color .from the hose 31 preparatory to the delivery thereto of paint of a different color comprises a cylinder 50 in which a piston 51, FIG. 2, is slidable axially between stops 52, 53 which determine the stroke of the piston thereby to form with the cylinder 50 gas and solvent chambers 54, 55 on opposite sides of the piston. The solvent chamber 55 has a solvent inlet 56 connectable, as by a pipe 57, FIG. 1, with a source, not shown, of solvent, and a solvent outlet 58 connectable, as by a pipe 59 and a solvent delivery-valve 590, with the purging solvent port 22 of the selector and valve device. First control means, shown as a solenoidoperated pneumatic valve 60 is operable to control the flow of solvent to the solvent chamber 55 and second control means, shown as a solenoid-operated pneumatic valve 61 and a preceding gas regulator 62, connect a source, not shown, of compressed air with connector means fitted to the cylinder 50. As shown in FIG. 2 the connector means includes a plug 63 which is screwed into the cylinder at 64 to be adjustable axially of the cylinder to determine the volume of the gas chamber 54. The stops 52, 53 are located in the plug, the stop 53 being formed by the stop 52 being a member screwed into the plug to be adjustable axially of the plug to determine the volume of the solvent chamber 55 and the stop 53 being the end of an extension 153 of the stop 52, the stop 53 engaging the bottom of a spring-housing 151 formed in the stem 251 of the piston 51. The stem 251 is slidable in the plug 63. The stop 52 is locked in an adjusted position thereof by a locking member 65 also screwed into the plug. The valve 61 and regulator 62 are included in a pipe line 66, FIG. 1, which is connected with a source, not shown, of compressed air and with an adaptor 67 fitted to the plug 63 and through which compressed air passes via bores 68 in the plug into the air chamber 54. The settings x and y, FIG. 2, are efi'ected respectively to suit the length of the hose 31 and the entrapped air volume to give the necessary residual pressure to overcome the resistance of the paint circuit from the selector and valve device to the spray guns, according to the type of paint, nozzle size, and emission rate and are best obtained empirically.

A spring 69, FIG. 2, tending to urge the piston 51 towards the solvent chamber-55 is housed in the housing 151 and is arranged to exert on the piston a pressure approximating to that of the frictional forces of the piston on the walls of the cylinder 50.

When the programming unit referred to above instructs a change of color the sequence is as follows: The solvent delivery valve 59a is already closed and the valve 60 is instructed to open to allow solvent to pass into the solvent chamber 55 and to force the piston upwards against the stop 52. The valve 60 is then closed and the valve 61 is opened to put regulated'airpressure, that is the same as paint pressure, on to the upper side of the piston 51. Valve 61 is then closed. This" sequence takes place timewise between the signal to change color being given and the signal for the arm 25 to move into alignment with the solvent port 22. Thesignal which initiates movement of the arm 25 also opens the valve 59a. During this period the gun continues to spray, the flexibility of the hose ensuring a steady flow of paint while the arm 25 is moved from the color port to the port 22. When the arm 25 is connected to port 22 the air pressure on the upper side of the piston 51 pressurizes the solvent in the solvent chamber and in turn the residual paint in the hose 31 thus causing it to pass through the spray gun nozzle with a substantially constant rate of emission the same as that when the arm 25 was connected to the paint rt. At the end of the purging operation the valve 59a is closed, the valve 60 and 61 being already closed, and the arm 25 is rotated into alignment with'the port from which the paint of next color is to be delivered.

Iclaim:

1. Apparatus for controlling the operation of a spray gun, comprising a single hose connected to the gun and arranged to connect the gun to any one of a plurality of paint delivery ports and with a solvent delivery port from which a solvent is delivered to the gun during disconnection of the hose from one paint delivery port and connection of the hose with another of the paint delivery ports, and a solvent pressure controlling device included in a solvent delivering line to the solvent port and operable when the hose connects the solvent delivery port with the hose to maintain the rate of emission from the gun of residue paint in the hose at a pressure substantially the same as that at which paint is emitted from the gun when the hose connects the gun to a paint delivery port.

2. Apparatus according to claim 1, wherein the solvent pressure controlling device comprises a cylinder, a piston slidable axially within the cylinder between stops determining the stroke of the piston thereby to form in the cylinder gas and solvent chambers on opposite sides of the piston, a solvent inlet to the solvent chamber connectable with a source of solvent, a solvent outlet from the solvent chamber connectable with said-solvent delivery port, control means operable to control the flow of solvent to the solvent chamber to urge the piston into the gas chamber, and connector means connectable with a source of pressurized gas and arranged to admit gas to the gas chamber. thereby to feed the solvent through the solvent outlet thereby to effect said emission from the gun of residue paint in the hose.

3. Apparatus according to claim 2, wherein the connector means includes ,a plug adjustable axially of the cylinder to determine the volume of the gas chamber.

4. Apparatus according to claim 2, wherein the connector means includes a solenoid-operated pneumatic valve preceded by a gas regulator.

5. Apparatus according to claim 3, wherein the stops are located in the plug and one of the stops is adjustable axially of the plug to determine the volume of the solvent chamber.

6. Apparatus according to claim 5, wherein a spring tending to urge the piston towards the solvent chamber exerts on the piston a pressure approximating that of the frictional forces of the pistonon the walls of the cylinder.

7. Apparatus according to claim 2, wherein the control means comprises a solenoid-operated pneumatic valve.

8. Apparatus according to claim 3, wherein the conv exerts on the piston a pressure approximating that of: the frictional forces of the piston on the walls of the cylinder. 

1. Apparatus for controlling the operation of a spray gun, comprising a single hose connected to the gun and arranged to connect the gun to any one of a plurality of paint delivery ports and with a solvent delivery port from which a solvent is delivered to the gun during disconnection of the hose from one paint delivery port and connection of the hose with another of the paint delivery ports, and a solvent pressure controlling device included in a solvent delivering line to the solvent port and operable when the hose connects the solvent delivery port with the hose to maintain the rate of emission from the gun of residue paint in the hose at a pressure substantially the same as that at which paint is emitted from the gun when the hose connects the gun to a paint delivery port.
 2. Apparatus according to claim 1, wherein the solvent pressure controlling device comprises a cylinder, a piston slidable axially within the cylinder between stops determining the stroke of the piston thereby to form in the cylinder gas and solvent chambers on opposite sides of the piston, a solvent inlet to the solvent chamber connectable with a source of solvent, a solvent outlet from the solvent chamber connectable with said solvent delivery port, control means operable to control the flow of solvent to the solvent chamber to urge the piston into the gas chamber, and connector means connectable with a source of pressurized gas and arranged to admit gas to the gas chamber thereby to feed the solvent through the solvent outlet thereby to effect said emission from the gun of residue paint in the hose.
 3. Apparatus according to claim 2, wherein the connector means includes a plug adjustable axially of the cylinder to determine the volume of the gas chamber.
 4. Apparatus according to claim 2, wherein the connector means includes a solenoid-operated pneumatic valve preceded by a gas regulator.
 5. Apparatus according to claim 3, wherein the stops are located in the plug and one of the stops is adjustable axially of the plug to determine the volume of the solvent chamber.
 6. Apparatus according to claim 5, wherein a spring tending to urge the piston towards the solvent chamber exerts on the piston a pressure approximating that of the frictional forces of the piston on the walls of the cylinder.
 7. Apparatus according to claim 2, wherein the control means comprises a solenoid-operated pneumatic valve.
 8. Apparatus according to claim 3, wherein the connector means includes a solenoid-operated pneumatic valve preceded by a gas regulator.
 9. Apparatus according to claim 4, wherein the stops are located in the plug and one of the stops is adjustable axially of the plug to determine the volume of the solvent chamber.
 10. Apparatus according to claim 9, wherein a spring tending to urge the piston towards the solvent chamber exerts on the piston a pressure approximating that of the frictional forces of the piston on the Walls of the cylinder. 